A vehicle entering the atmosphere of a planet will do so at hypersonic speeds. The vehicle will need to decelerate and maneuver through that atmosphere while protecting its payload from excessive heating. As a consequence, the design of the vehicle shape so as to provide optimal aerodynamic lift and drag properties while minimizing convective and radiative heating to the vehicle outer surfaces is critical to its survival and performance. Optimizing the aerodynamic performance of such a vehicle allows greater latitude in choice of entry trajectory and timing, while minimizing heating levels may provide a greater choice of thermal protection materials and allow minimization of thermal protection system weight, thereby allowing greater payload and maximizing the probabilities of survival.
Two types of atmospheric entry shapes are in current use: winged and blunt-body. Blunt body shapes allow lower construction and maintenance costs and have proven more robust than winged shapes. However, blunt body atmospheric entry vehicles also tend to provide lower aerodynamic performance (e.g., net lift) than do winged shapes. Blunt bodies to date have been primarily simple geometric symmetric shapes, such as the Apollo shape which has a circular/torus symmetric cross-section heat shield, or the 70 degree sphere-cone heat shield such as typically used for many Mars missions.
Improvement of the aerodynamic performance of blunt body entry vehicles is highly desirable to allow a wider entry corridor, to allow greater cross-range capability for landing at a desired location, and to provide additional, favorable impacts on mission operations.
Blunt body atmospheric entry vehicles tend to consist of a heat shield fore-body, which faces the wind and encounters the high levels of heating associated with entry, and an aft-body section, which covers the payload region. Particularly at hypersonic speeds, Mach 5 and above, the fore-body heat shield design, including its shape, is critical in establishing the aerodynamic and aerothermal performance of the vehicle.
What is needed is a shape for a shell structure for a re-entry vehicle that, during atmospheric entry, generates near-optimal associated lift forces and has improved heat transfer and pressure characteristics. Preferably, the shape should be convex and should be describable by a relatively small number of geometric parameters that can be varied, during design of the optimal shape for the expected environment.